How to use JavaScriptSerializer with ASP.NET 2.0?: json, asp.net 2.0

How to use JavaScriptSerializer with ASP.NET 2.0?

I am developing asp.net 2.0 with vb code-behind in Visual Studio 2005.
I have a webmethod in my aspx code-behind that accepts a single parameter defined as integer and is supposed to return a string. (see code below)
I call this webmethod using jQuery (see code below)

I was manually concatenating a json response for my return from the webmethod but wasn't getting the expected results in formatting. But I was seeing the results of my methods execution when using FireBug. So I thought I'd try using System.Web.Script.Serialization.JavaScriptSerializer to serialize the return.
(see code below) But now I get a 500 Internal Server Error with the following message:

{"Message":"Conversion from string \"\" to type \u0027Integer\u0027 is not valid.","StackTrace":" at
Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger(String Value)\r\n at
PageName.GetClassDescription(String ClassID)","ExceptionType":"System.InvalidCastException"}

The Post looks like correct json for passing an integer: {'ClassID': 1}
I am using .Net Framework 2.0 (not 3.5) and calling the webmethod in an aspx, not a webservice in an asmx, page.

Could someone tell me why this happening?

$.ajax
        ({
            type: "POST",
            url: "Training_Add.aspx/GetClassDescription", 
            contentType: "application/json; charset=utf-8", 
            dataType: "json",
            data: "{'ClassID': " + ParseInt(classselected) + "} ",  //have also sent without the parseint-no difference
            success: function(msg) {   
                     CallSucccess(msg);   
                 },
            error: onError
        });
 
in webmethod:
<Services.WebMethod()> Public Shared Function GetClassDescription(ByVal ClassID As Integer) As String
        Dim jsSerializer As New System.Web.Script.Serialization.JavaScriptSerializer
        Dim ReturnVal As New Returns
                    ReturnVal.ParameterName = "ClassDescription"
                    ReturnVal.ParameterValue = ClassDescription.Value
                    strClassDescription = jsSerializer.Serialize(ReturnVal)
GetClassDescription = strClassDescription

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How to use JavaScriptSerializer with ASP.NET 2.0?

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json

asp.net 2.0

JavaScript

.NET Framework 2.x

Asynchronous Javascript and XML (AJAX)

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